Ion implantation or doping is one of several processes performed for, among others, manufacturing electronic devices. As known in the art, a beam-line ion implantation system may be used to perform ion implantation. A block diagram of a conventional ion implanter is shown in FIG. 1. The conventional ion implantation system 100 may comprise an ion source 104; a plurality of beam-line components; and an end station. As known in the art, the ion source 104 may be used to generate ions of desired species 102. The generated ions may be extracted from the ion source 104 by the beam-line components 105. Much like a series of optical lenses that manipulate a light beam, the beam-line components 105 manipulate the ions 102 into an ion beam 102 and steer the beam 102 towards an end station 110 where a wafer 106 and a platen 108 supporting the wafer 106 are located. The ion beam directed toward the end station is incident on the wafer 106 and ion implantation may be performed.
The ion implantation may also be performed using a system known as a plasma doping (“PLAD”) or plasma immersion ion implantation (“PIII”) system. In the PLAD system, the wafer 106 and the platen 108 supporting the wafer 106 are placed in a process chamber. Meanwhile, process gas containing a desired species is into a plasma source of PLAD system 200. In some systems, the plasma source is adjacent to the process chamber. In other systems, the plasma source is removed and remote from the process chamber. The process gas is then converted into plasma 210 containing electrons, ions 202 of the desired species, neutrals, and/or residuals. The wafer 106 may be biased, and ions 202 of the desired species may be implanted into the wafer 106.
The platen 108 may be used to support the wafer 106 during ion implantation. The platen 108 may comprise a plurality of electrodes (not shown) that electrostatically clamp the wafer 106 to the platen 108. In some cases, platen 108 may enable the wafer 106 to move in several directions (e.g. translate, rotate, tilt, etc. . . . ).
The platen 108 may be used to control several ion implantation parameters. For example, the platen 108 may be used to maintain the temperature of the wafer 106 at a desired level. Because the ion implantation process is an energetic process, temperature of the wafer 106 may be elevated to a level beyond that is desired. Generally, the platen 108 is used to prevent overheating of the substrate. The conventional platen may have a cooling recess (not shown) which, along with the mounted wafer 106, may define a cooling region (not shown). Cooling gas may be introduced into the cooling region and maintained at a predetermined pressure such that the gas may contact the wafer 106 and cool the wafer 106.
Another implant parameter that can be controlled using the platen 108 includes preventing excessive charge buildup in the wafer 106. As known in the art, excessive charge may build up in the wafer 106 as the wafer 106 is bombarded with charged ions. Excessive charge buildup may cause arcing and lead to catastrophic failure of the wafer 106. In addition, the charge buildup may hinder the wafer 106 from being de-clamped from the platen 108 after completion of the ion implantation process. To avoid excess charge buildup, the wafer 106 and 206 may contain one or more ground circuits (not shown) that electrically connects the wafer 106 to the ground and reduce excessive charge buildup.
In the conventional platen 108, parts of the platen 108 directly contact the wafer 106. Such contacts may generate debris. The debris may drift to the front side of the wafer 106, the side on which the ion beam is incident. Debris near the front side of wafer 106 may be disadvantageous as the debris may interfere with the implantation process and, ultimately, contribute to less than optimum devices. Accordingly, an improved platen is needed.